The present invention relates to a device for tapping bores, especially for tapping blind bores such as are often found at the parting line between two components.
There are many instances where blind bores must be tapped. One of these instances is in the case where the blind bores are provided at the parting line between two components, for instance between two halves of a reactor housing, two halves of a turbine housing or the like, where one of the halves must be provided with blind bores while the other half is provided with open-ended bores through which bolts are inserted to be threaded into the blind bores. The diameters of the tapped threads in blind bores, especially of halves of turbine housings, reactor housings or the like, are usually on the order of between substantially 60 and 130 millimeters diameter, the threaded having a pitch of between 6 and 9 millimeters. It is the present practice of the industry to tap such bores with expensive specialty taps. The tapping can be carried out only very slowly and frequently the chips of material which are dislodged during the tapping and which become crowded into the flutes of the tap, especially as the tap begins to approach the bottom of the blind bore, cause the tap to break. Moreover, such bores must be provided with a hole expansion which makes the formation of the threads even more difficult and expensive than it already is, and which tends to weaken the workpiece in addition.
Furthermore, there is always the danger that the tap may not run strictly coaxially with the previously drilled bore if the tap is supported on and rotated by one of the conventional drilling machines having an arm that is swung from a position laterally of the workpiece over the latter. In this case it is well possible that the workpiece may have to be discharged.